Keel...another term that I don't see the logic behind the name. Keel, in other things like ships and airplanes, means a longitudinal prominent/primary structural element. Nothing in Websters would lead anyone that held one of these in their hand to name it a keel, IMO. A tiny little triangular filler doesn't seem to meet the definitions there.
This little thing oughta be called a 'nib' or a chiclet or some such small,insignificant defining name. BTW, thats an original nib from a 12g Parker.
Anyway, if a gun was cut and filling the barrel/rib voids was needed, putting in a little piece of metal would be a piece of cake, for me. Even pulling muzzles together without reblueing should be pretty easy using some wire for pressure and a torch.
On the other comments about barrels not touching at the muzzle, The Winchester 23 in 410 and 28g in shorter lengths don't touch at the muzzles by a long shot. Neither did a CSM/Win 21 410 I recently worked on.
